Method and device for detecting and generating synchronization signal for device-to-device wireless communication

ABSTRACT

Provided is a method of generating a Device-to-Device Synchronization Signal (D2DSS) by a terminal according to an embodiment of the present disclosure. The method includes determining a service attribute for identifying whether the terminal is serviced by at least one base station; and generating a D2DSS for identifying whether the terminal is serviced by the base station, based on the determination result. In addition, provided is a method of configuring D2D synchronization by a terminal according to an embodiment of the present disclosure. The method includes receiving a signal from at least one base station or another device; determining whether a synchronization signal is detected from the received signal; and when the synchronization signal is detected, configuring synchronization with the another device based on the timing reference of the detected synchronization signal.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to and claims priority from and thebenefit under 35 U.S.C. §119(a) of Korean Patent Application No.10-2014-0010765, filed on Jan. 28, 2014 and No. 10-2014-0058917, filedon May 16, 2014, which are hereby incorporated by reference for allpurposes as if fully set forth herein.

TECHNICAL FIELD

The present application relates to a method and device for measuring andgenerating a synchronization signal for device-to-device wirelesscommunication. More particularly, the present application relates to asynchronization signal design in a wireless communication system, andthe objective of the present application is to provide a method anddevice which can design a synchronization signal for acquiringsynchronization in communication between device-to-device supportterminals and can acquire synchronization of a terminal using the same.

BACKGROUND

The 3rd Generation Partnership Project (3GPP), the standards group forasynchronous cellular mobile communication, is studying the support forwireless communication between terminals or devices, namely,Device-to-Device (D2D) communication using the Long Term Evolution (LTE)system standards, as well as conventional wireless communication betweena base station and a terminal. In particular, one important functionwhich 3GPP requires of D2D communication is a public safety servicesupport function. That is, even in the case of emergency (such as in anatural disaster) in which a normal network service cannot be provided,the D2D communication has to be able to support LTE based wirelesscommunication within or between police, firemen, and government agents.

In general, for smooth communication service support in a wirelesscommunication system, it is necessary to acquire a tinning reference tobe used for signal transmission or reception of terminals in a system,namely, to acquire time synchronization. Also, in an LTE system, when acellular network service is operating normally, terminals inside theservice region of a base station can receive a Primary SynchronizationSignal (PSS)/Secondary Synchronization Signal (SSS) transmitted througha downlink from the base station to acquire synchronization. However, insituations in which the cellular network service cannot be normallyprovided due to an emergency as described above, it is impossible toacquire synchronization from the base station.

Accordingly, there is a need for a synchronization acquisition means forsupporting communication between devices even in situations in whichcellular network service cannot be normally provided due to emergencies.

SUMMARY

To address the above-discussed deficiencies, it is a primary object toprovide a method and device for measuring and generating asynchronization signal for device-to-device wireless communication.

The present disclosure provides a D2DSS signal design plan capable ofdistinguishing the type of a D2DSS transmission subject such that aterminal to transmit a D2DSS in the D2D communication environmentdescribed above in the background can efficiently select a timingreference to use when detecting a plurality of D2DSSs having differenttiming references.

In addition, another aspect of the present disclosure is to provide amethod and device for acquiring a timing reference when transmitting aD2DSS using the designed D2DSS.

The technical subjects pursued in the present disclosure may not belimited to the above mentioned technical subjects, and other technicalsubjects which are not mentioned may be clearly understood, through thefollowing descriptions, by those skilled in the art of the presentdisclosure.

In accordance with one aspect of the present disclosure, a method ofgenerating a Device-to-Device Synchronization Signal (D2DSS) by aterminal is provided. The method includes determining a serviceattribute for identifying whether the terminal is serviced by at leastone base station; and generating a D2DSS for identifying whether theterminal is serviced by the base station, based on the determinationresult.

In accordance with another aspect of the present disclosure, a device ofa terminal for generating a Device-to-Device Synchronization Signal(D2DSS) is provided. The device includes a transmission or receptionunit that communicates with at least one base station or device; and acontroller that determines a service attribute for identifying whetherthe terminal is serviced by at least one base station and makes acontrol to generate a D2DSS for identifying whether the terminal isserviced by the base station, based on the determination result.

In accordance with another aspect of the present disclosure, a method ofconfiguring D2D synchronization by a terminal is provided. The methodincludes: receiving a signal from at least one base station or anotherdevice; determining whether a synchronization signal is detected fromthe received signal; and when the synchronization signal is detected,configuring synchronization with the another device based on the timingreference of the detected synchronization signal.

In accordance with another aspect of the present disclosure, a terminalfor Device-to-Device (D2D) synchronization configuration is provided.The terminal includes a communication unit that transmits or receives asignal to or from at least one base station or another device; and acontroller that receives a signal from the at least one base station orthe another device; determines whether a synchronization signal isdetected from the received signal, and when the synchronization signalis detected, makes a control to configure synchronization with theanother device based on the timing reference of the detectedsynchronization signal.

As described above, the present disclosure provides a method and devicefor measuring and generating a synchronization signal fordevice-to-device wireless communication.

Through the D2DSS design method according to the embodiment of thepresent disclosure, a terminal to transmit a D2DSS can distinguish thetypes of D2DSS transmission subjects when detecting a plurality ofD2DSSs. Based on this, the terminal can effectively select the timingreference of the D2DSS transmission subject to which the D2DSStransmission timing reference thereof is fit.

Furthermore, in cases where the D2DSS design method according to thepresent disclosure is applied, D2DSS design is easy when D2Dcommunication is introduced into an LTE system.

Effects obtainable from the present disclosure may not be limited to theabove mentioned effects, and other effects which are not mentioned maybe clearly understood, through the following descriptions, by thoseskilled in the art of the present disclosure.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an example of D2DSS signal design according toembodiments of the present disclosure;

FIG. 2 illustrates an exemplary process for detecting a synchronizationsignal according to embodiments of the present disclosure;

FIG. 3 illustrates an exemplary process for detecting and transmittingD2DSS according to embodiments of the present disclosure;

FIG. 4 illustrates an exemplary process for detecting a synchronizationsignal and performing synchronization configuration according toembodiments of the present disclosure;

FIG. 5 illustrates an exemplary process for detecting and transmitting asynchronization signal according to embodiments of the presentdisclosure;

FIG. 6 illustrates an exemplary process for detecting and transmitting asynchronization signal according to embodiments of the presentdisclosure;

FIG. 7 illustrates an exemplary process for detecting a synchronizationsignal and transmitting the synchronization signal based on a hop numberaccording to embodiments of the present disclosure;

FIG. 8 illustrates an exemplary process for detecting a synchronizationsignal and transmitting the synchronization signal based on a receptionlevel according to embodiments of the present disclosure;

FIG. 9 illustrates a block diagram of a reception block of a D2DSStransmission terminal according to embodiments of the presentdisclosure; and

FIG. 10 illustrates a block diagram of a transmission block of a D21?SStransmission terminal according to embodiments of the presentdisclosure.

DETAILED DESCRIPTION

FIGS. 1 through 10, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communications system.Hereinafter, various embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Itshould be noted that the same elements will be designated by the samereference numerals although they are shown in different drawings.Further, a detailed description of a known function and configurationwhich may make the subject matter of the present disclosure unclear willbe omitted. Hereinafter, it should be noted that only the descriptionswill be provided that may help understanding the operations provided inassociation with the various embodiments of the present disclosure, andother descriptions will be omitted to avoid making the subject matter ofthe present disclosure rather unclear.

Although the following detailed description of embodiments of thepresent disclosure is directed to the 3GPP LTE standard, it can beunderstood by those skilled in the art that the present disclosure canalso be applied to any other communication system having similartechnical backgrounds and channel formats, with slight modifications,without substantially departing from the scope of the presentdisclosure.

Hereinafter, a method of designing a discovery signal and a method anddevice for allocating a discovery signal resource and detecting adiscovery signal, according to exemplary embodiments of the presentdisclosure, is described in detail.

In addition, a physical layer signal structure of an LTE system isconsidered for convenience of description. A radio frame having a unitof 10 ms is present in the physical layer signal structure of the LTEsystem. The radio frame consists of ten subframes having units of 1 msand one subframe consists of fourteen symbols.

In the 3GPP standards, a separate synchronization signal for D2Dcommunication is introduced as a means for acquiring synchronizationbetween D2D terminals to satisfy public safety service supportrequirements. A terminal transmits a D2DSS through resources configuredfor uplink D2D communication. Other surrounding terminals receive theD2DSS from the terminal and acquire synchronization. Here, the D2Dterminals retain a function of receiving an uplink signal.

Before transmitting the D2DSS, the terminal attempts to detect PSS/SSStransmitted from a base station or a D2DSS transmitted from anotherterminal. If both types of synchronization signals are not detected, theterminal attempting the detection recognizes that there is no subjectaround for providing a timing reference, and can provide a timingreference for D2D communication by transmitting the D2DSS according tothe timing reference thereof. If the terminal attempting the detectionsucceeds in detecting the PSS/SSS from the base station or the D2DSSfrom another terminal, the terminal, before transmitting the D2DSS, cansynchronize a receiver thereof according to the timing reference of thesubject having transmitted the detected synchronization signal.

While performing the above-described operation, the terminal detects aplurality of synchronization signals having different timing referencesbefore transmitting the D2DSS. In this case, a rule is required todetermine the timing reference of the synchronization signal for thetransmission of the D2DSS. One of the methods under discussion in theLTE standards is to determine the priority of the timing reference towhich the terminal preferentially conforms when transmitting the D2DSS,depending upon the type of subject having transmitted a synchronizationsignal.

For example, when a D2DSS transmission terminal detects twosynchronization signals, one being a PSS/SSS which a base station hastransmitted through a downlink and the other being a D2DSS which anotherterminal has transmitted through an uplink, the terminal transmittingthe D2DSS can determine to use the timing reference for the PSS/SSS ofthe base station. In another example, when a D2DSS transmission terminaldetects two synchronization signals, one being a D2DSS which a terminalinside a normal network operation region has transmitted and the otherbeing a D2DSS which a terminal outside the normal network operationregion has transmitted, the terminal transmitting the D2DSS candetermine to transmit the D2DSS using the timing reference for the D2DSSwhich the terminal inside the normal network operation region hastransmitted.

In case of emergency, one-to-many communications, namely, broadcastcommunication for a particular group performing public safety work, forexample a group of police or firemen or the entire group, is moreefficient than one-to-one communication between mobiles stations. In thecurrent Release-12 (Rel-12) step, the 3GPP has also agreed to usebroadcast communication as a D2D communication scheme. In addition,physical layer feedback of a closed loop method, such as hybridautomatic repeat request (HARQ) acknowledge character (ACK) ornegative-acknowledge character (HACK), is not likely to be applied inview of characteristics of one-to-many communication.

Wireless resources used by a transmission terminal in D2D communicationcan be allocated by one of the two following methods. First, in thecentral resource allocation method, the transmission terminal can beallocated with wireless resources to use, by a particular resourceallocation subject. The particular resource allocation subject can serveas a base station of the cellular communication, and when a networkcannot normally provide a service, a particular terminal can perform theresource allocation function. In this case, it is possible to performD2D communication without collision of wireless resources by schedulingthe wireless resources of each terminal inside the region of theresource allocation terminal.

However, in cases using the central allocation method, selecting theparticular resource allocation terminal is separately determined, andsince a terminal performing resource allocation has to support thefunction of the base station, a burden due to the complexity of theterminal increases. In addition, it is necessary to define a controlchannel for transmitting or receiving the resource allocationinformation. Furthermore, in cases where a plurality of terminalsperforming resource allocation are adjacent to each other, mediationinformation between the resource allocation terminals is required toprevent resource allocation collision of the terminals in the adjacentregions. Although the base station can transfer the mediationinformation using a wired network, a separate physical channel or signalhas to be defined for exchange of the mediation information between theresource allocation terminals.

Second, in the distributed resource allocation method, a transmissionterminal can select a wireless resource to use. The process in which thetransmission terminal selects the wireless resource can be generallyperformed through the Channel Sense Multiple Access (CSMA) or CollisionAvoidance (CA) method. That is, the transmission terminal performschannel sensing for a wireless resource region configured for D2Dcommunication to identify whether the current corresponding wirelessresource is used for D2D communication of another terminal. If it isdetermined that the corresponding wireless resource is occupied byanother terminal, the transmission terminal continues to perform thechannel sensing to discover an available wireless resource without usingthe corresponding wireless resource. If it is determined that thecorresponding wireless resource is empty, the transmission terminal cantransmit a signal thereof using the corresponding wireless resource.Here, the transmission terminal has to indispensably transmit a channelsensing signal for informing that the transmission terminal is using thewireless resource, to other terminals performing the channel sensing.The channel sensing signal can have a sequence based signal structuresimilar to a random access preamble or a Reference Signal (RS).

In the distributed resource allocation method, there is a possibility ofresource collision in which a plurality of transmission terminalsperforming the channel sensing determine that a particular wirelessresource is empty and simultaneously transmit a signal thereof. Incontrast, since a resource allocation terminal acting as a base stationis not required, there is no burden for the complexity of the terminal.Furthermore, since the aforementioned resource allocation and themediation information between the resource allocation terminals are notnecessarily required in the central resource allocation method, theoperation can be performed only with minimum signaling through a channelsensing signal. In particular, random back-off can be applied toalleviate the aforementioned resource collision between the transmissionterminals. After the channel sensing is performed, when it is determinedthat a wireless resource is empty, the channel sensing continues to beperformed for a back-off time randomly selected for each terminal. As aresult, when the channel sensing signal transmitted by another terminalis not detected so that it is determined that the corresponding wirelessresource is empty, the terminal starts transmission. In contrast, whenit is determined that the corresponding wireless resource is not empty,the terminal stops the back-off.

A method of designing a D2DSS according to n embodiment of the presentdisclosure includes dividing a set of cyclic shift values that at leastone sequence constituting a D2DSS can have into a plurality of subsets;making the divided subsets one-to-one correspond to the types of D2DSStransmission subjects; and generating, by a terminal transmitting theD2DSS, at least one sequence constituting the D2DSS by selecting atleast one of the cyclic shift values pertaining to the subsetcorresponding to the type of transmission subject to which the terminalbelongs.

A method of designing a D2DSS according to an embodiment of the presentdisclosure includes dividing a set of root index values that at leastone Zadoff-Chu (LC) sequence constituting a D2DSS can have into aplurality of subsets; making the divided subsets correspond to the typesof D2DSS transmission subjects one-to-one; and generating, by a terminaltransmitting the D2DSS, at least one ZC sequence constituting the D2DSSby selecting at least one of the root index values pertaining to thesubset corresponding to the type of transmission subject to which theterminal belongs.

A method of designing a D2DSS according to embodiment of the presentdisclosure includes differently configuring locations of physical layerresources to which one or more sequences constituting a D2DSS aremapped, according to the types of D2DSS transmission subjects; andgenerating and mapping, by a terminal transmitting the D2DSS, at leastone sequence constituting the D2DSS at the location of the physicallayer resource corresponding to the type of transmission subject towhich the terminal belongs.

A method of designing a D2DSS according to an embodiment of the presentdisclosure includes differently determining relative locations ofphysical layer frequency resources to which at least two sequencesconstituting a D2DSS are mapped, according to the types of D2DSStransmission subjects; and generating and mapping, by a terminaltransmitting the D2DSS, at least two sequences constituting the D2DSS atthe relative location of the physical layer frequency resourcecorresponding to the type of transmission subject to which the terminalbelongs.

A method of transmitting a D2DSS by a transmission terminal according toan embodiment of the present disclosure includes recognizing the type ofa synchronization signal transmission subject by a synchronizationsignal detected by the transmission terminal; generating and mapping aD2DSS to a physical layer resource according to the type of therecognized synchronization signal transmission subject; and transmittingthe D2DSS using a timing reference according to the detectedsynchronization signal.

A method of transmitting a D2DSS by a transmission terminal according toan embodiment of the present disclosure includes recognizing the typesof synchronization signal transmission subjects from a plurality ofsynchronization signals detected by the transmission terminal; selectingthe type of synchronization signal transmission subject transmitting thesynchronization signal, the timing reference of which is to be used,among the types of recognized synchronization signal transmissionsubjects; generating and mapping the D2DSS to a physical layer resourceaccording to the selected type of synchronization signal transmissionsubject; and transmitting the D2DSS using the timing reference accordingto the selected synchronization signal.

A method of designing a D2DSS according to an embodiment of the presentdisclosure includes dividing a set of cyclic shift values, which atleast one sequence constituting a D2DSS can include, into a plurality ofsubsets; making each of the divided subsets correspond to the turn of asynchronization signal relay hop indicated by the corresponding D2DSSone-to-one; and generating, by a terminal transmitting the D2DSS, atleast one sequence constituting the D2DSS by selecting at least one ofthe cyclic shift values pertaining to the subset corresponding to theD2DSS relay hop number thereof.

A method of designing a D2DSS according to an embodiment of the presentdisclosure includes dividing a set of root index values which at leastone Zadoff-Chu (ZC) sequence constituting a D2DSS can include into aplurality of subsets; making each of the divided subsets correspond tothe turn of a synchronization signal relay hop indicated by thecorresponding D2DSS one-to-one; and generating, by a terminaltransmitting the D2DSS, at least one ZC sequence constituting the D2DSSby selecting at least one of the root index values pertaining to thesubset corresponding to the D2DSS relay hop number thereof.

A method of designing a D2DSS according to an embodiment of the presentdisclosure includes differently configuring locations of physical layerresources to which one or more sequences constituting a D2DSS are mappedaccording to the turn of a D2DSS relay hop to which the pertinent D2DSScorresponds; and generating and mapping, by a terminal transmitting theD2DSS, at least one sequence constituting the D2DSS to the location ofthe physical layer resource corresponding to the D2DSS relay hop numberthereof.

Hereinafter, embodiments of the present disclosure will be described inmore detail with reference to the accompanying drawings.

FIG. 1 illustrates an example of D2DSS signal design according toembodiments of the present disclosure. The embodiment D2DSS signaldesign shown in FIG. 1 is for illustrations only. Other embodimentscould be used without departing from the scope of the presentdisclosure.

Referring to FIG. 1, in an embodiment of the present disclosure, aDevice-to-Device Synchronization Signal (D2DSS) can be constituted bytwo sequences. In certain embodiments, the first sequence 100 includes afrequency length corresponding to subcarriers, except for subcarriersthat are not used among frequency resources, configured with a length ofK Resource Blocks (RBs) and a length of time corresponding to M symbols.In certain embodiments, the RB is a frequency resource allocation unitconstituted by twelve subcarriers, and K can be determined as onepositive integer. M of M symbols can be determined to have a value of atleast ‘1,’ and the symbol can be an Orthogonal Frequency DivisionMultiple Access (OFDMA) symbol or a Single Carrier Frequency DivisionMultiple Access (SC-FDMA) symbol. In addition, the first sequence 100includes a structure in which two short sequences 101 and 102 alternatewith each other in units of the subcarrier on a frequency axis.

The second sequence 103 starts at the symbol separated L symbols apartfrom the first sequence 100. In certain embodiments, L has a value of‘0’ or a positive integer. The second sequence 103 can be mapped to thesame frequency range as the first sequence 100 over N symbol timeperiod. In certain embodiments, the value of N is the same as the valueof M.

In certain embodiments of the present disclosure, a D2DSS is transmittedat least two times within a radio frame having units of 10 ms. Forexample, the D2DSS can be transmitted in subframe 0 and subframe 5 ofone radio frame. A terminal can attempt to detect the second sequence103 first, when detecting the D2DSS. In certain embodiments, the secondsequence 103 is employed for acquiring subframe unit synchronizationusing the same sequence at every D2DSS transmission time point withinthe radio frame. The second sequence 103 can have a Zadoff-Chu (ZC)sequence format. In addition, the ZC sequence can be generated accordingto one index value in a preconfigured set of root indices.

The terminal having acquired the subframe unit synchronization bydetecting the second sequence 103 of the D2DSS successively attempts todetect the first sequence 100 located L symbols apart from the secondsequence 103. In certain embodiments, the first sequence 100 isconstituted by two short sequences 101 and 102, each of which caninclude an m-sequence based format. In addition, assuming that the D2DSSis transmitted in subframe 0 and subframe 5 per radio frame, subcarriersignals to which the first sequence 100 is mapped can include valuesgiven by Equation 1 below.

$\begin{matrix}{{d\left( {2n} \right)} = \left\{ {{\begin{matrix}{{s_{0}^{(m_{0})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 0} \\{{s_{1}^{(m_{1})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 5}\end{matrix}{d\left( {{2n} + 1} \right)}} = \left\{ \begin{matrix}{{s_{1}^{(m_{1})}(n)}{c_{1}(n)}{z_{1}^{(m_{0})}(n)}} & {{in}\mspace{14mu} {subframe}{\mspace{11mu} \;}0} \\{{s_{0}^{(m_{0})}(n)}{c_{1}(n)}{z_{1}^{(m_{1})}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 5}\end{matrix} \right.} \right.} & {{Equation}\mspace{14mu} 1}\end{matrix}$

in Equation 1 above, d(*) denotes a subcarrier transmission signal towhich the first sequence 100 is mapped, and n has a different rangeaccording to K and the number of unused. subcarriers 104. For example,if K=6 and the number of unused subcarriers 104 is ‘10,’ n can include avalue ranging from ‘0’ to (12*K−10)/2−1=30. Consequently, d(2n) denotesan even subcarrier to which the first sequence 100 is mapped, andd(2n+1) denotes an odd subcarrier to which the first sequence 100 ismapped.

In addition, s₀ ^((m0)) and s₁ ^((m1)) represent two short m-sequencess₀ and s₁ having a length of 31, and m0 and m1 denote cyclic shiftvalues of m-sequence s₀ and s₁, respectively. c₀ and c₁ are m-sequencebased scrambling sequences, and different cyclic shift values aredetermined according to the root index value of the second sequence. z₁^((m0)) and z₁ ^((m1)) are also m-sequence based scrambling sequences,and an odd subcarrier signal is multiplied by cyclic shift values m₀ andm₁. As shown in Equation 1, the first sequence signal can be used foracquiring radio frame unit synchronization, since the signalstransmitted in subframe 0 and subframe 5 are different from each other.

In summary, the D2D terminal can acquire the subframe unitsynchronization through the detection of the second sequence of theD2DSS and can acquire the radio frame unit synchronization through thedetection of the first sequence. If a D2DSS signal is distinguishablydesigned according to the type of a D2DSS transmission subject based onthe aforementioned structure (for example, the first sequence 100 andthe second sequence 103 are differently configured according to theD2DSS transmission subject), the terminal to transmit the D2DSS canutilize the D2DSS to select the timing reference of the D2DSStransmission subject be used among a plurality of received D2DSSs.

In a different way, if a currently transmitted D2DSS signal isdistinguishably designed according to the number of D2DSS relay hops fortransmission thereof based on the aforementioned structure, the terminalto transmit the D2DSS can utilize the D2DSS to select the timingreference of the D2DSS to be used among a plurality of received D2DSSs.For example, a D2DSS can be transmitted using the timing reference basedon the D2DSS having the smallest number of synchronization signal relayhops among the detected D2DSSs.

According to certain embodiments of the present disclosure, a D2DSSsignal can be designed as follows. Since the range of cyclic shiftvalues, which two short m-sequences constituting the first sequence 100can have, is finite, available combinations of the cyclic shift valuesm₀ and m₁ are also determined as a finite set. Accordingly, a setconstituted by the combinations of m₀ and m₁ is divided into at leasttwo subsets, and each of the subsets corresponds to one of the types ofD2DSS transmission subjects one-to-one. For example, it is assumed thatm₀ and m₁ can include a value ranging from ‘0’ to ‘30’ and the types ofD2DSS transmission subjects are defined as a terminal inside a cellularnetwork service region and a terminal outside the cellular networkservice region. If there are 168 available combinations, namely, fromcombination 0 to combination 167, the combinations of m₀ and m₁ can bedifferentiated into two subsets as in Table 1 below.

Table 1 illustrates combinations capable of being used when a SecondarySynchronization Signal (SSS) of a cellular network is generated.However, the embodiment of the present disclosure is for illustrationonly. Other embodiments are not limited to the combinations listed inTable 1, and new combinations can be defined and used.

A set of combinations from number 0 to number 84 in Table 1 denotescombinations of m₀ and m₁, which terminals inside the cellular networkservice region use to generate the first sequence 100 when transmittinga D2DSS. In addition, a set of combinations from number 85 to number 167denotes combinations of m₀ and m₁ which terminals outside the cellularnetwork service region use to generate the first sequence 100 whentransmitting the D2DSS. The aforementioned method is not restricted tothese embodiments, and the number of subsets or the number of availablecombinations can be variously changed.

Table 2 is a reference table for illustrating another example of D2Ddesign. In a method of designing a D2DSS according to another embodimentof the present disclosure for achieving the objective, combinations,which are used to generate a Secondary Synchronization Signal (SSS) ofthe cellular network among the combinations of m₀ and m₁ in Table 1, areused to generate the first sequence 100 of a D2DSS transmitted by aterminal inside the cellular network service region. Separatecombinations are additionally defined which are not used to generate theSSS of the cellular network, and the corresponding separate combinationscan be used to generate the first sequence of a D2DSS transmitted by aterminal outside the cellular network service region. Table 2 belowlists the combinations.

A set of combinations from number 0 to number 167 in Table 2 denotescombinations used to generate an SSS transmitted by a base station.Terminals inside the cellular network service region are likely toconform to the timing reference of the base station to which theterminals belong, when transmitting a D2DSS. Accordingly, thecombinations used to generate the SSS received from the base station canalso be identically used to generate the first sequence of the D2DSS.Newly defined combinations from number 168 to number 188 in Table 2 canbe designed such that the terminals outside the cellular network serviceregion use the combinations when generating the first sequence 100 ofthe D2DSS. If the types of D2DSS transmission subjects are finelydivided, the two subsets shown in Table 2 can also be divided into lowerlevel subsets one-to-one corresponding to the finely divided types. Theaforementioned methods are not restricted to these embodiments, and thenumber of newly defined subsets or the number of available combinationscan be variously changed.

In certain embodiments, the D2DSS signal according to the embodiment canbe designed to inform of the number of D2DSS relay hops through whichthe D2DSS is transmitted or relayed. For example, the number of theD2DSS relay hop indicates the number of relaying of the D2DSS aftergeneration of the D2DSS. For example, the set constituted by thecombinations of m₀ and m₁ are divided into subsets corresponding to thenumber of D2DSS relay hops (for example, 0, 1, or 2), and the respectivesubsets correspond to the number of D2DSS relay hops corresponding tothe D2DSS one-to-one. For example, the combinations from number 0 tonumber 167 in Table 2 are used to transmit a D2DSS, with a timingreference established based on Primary Synchronization Signal(PSS)/Secondary Synchronizations Signal (SSS) received from a basestation. Since the corresponding terminal transmits the D2DSS firstusing the timing reference from the PSS or SSS, there is no previouslyrelay hopped D2DSS. That is, the corresponding terminal generates theD2DSS to transmit, based on the relay hop number 0. In certainembodiments, a terminal that detects no synchronization signal andtherefore transmits a D2DSS, can also generate the corresponding D2DSSbased on the D2DSS relay hop number 0. The combinations from number 168to number 177 are used to generate a D2DSS having the synchronizationsignal relay hop number of 1. The combinations from number 178 to number188 are used to generate a D2DSS having the synchronization signal relayhop number of 2.

In applying the methods of indicating the synchronization signal relayhop number using the D2DSS according to the aforementioned embodiments,the D2DSS can be subjected to Time Division Multiplexing (TDM) accordingto the synchronization signal relay hop number. If TDM methods are notapplied, D2DSSs indicating different synchronization signal relay hopnumbers can coexist at the same time point or in the subframe. In thecase where the TDM methods are not applied, a terminal transmitting theD2DSS can fail to simultaneously receive a D2DSS having differentsynchronization signal relay hop number from another terminal.

For example, assume that the maximum value of the synchronization signalrelay hop number is defined as 2 and the terminals apply the TDM methodwhen supporting the synchronization signal relay hop, The terminalreceiving D2DSSs of hop number 1 in time resources for the D2DSS ofsynchronization signal relay hop number 1 can smoothly perform thesynchronization signal relay hop by transmitting a D2DSS of hop number 2in different time resources for a D2DSS of synchronization signal relayhop number 2.

When a D2DSS is subjected to TDM methods for each synchronization signalrelay hop, at least one of the following methods can be applied.

In a first method, a mapping rule can be previously defined to map aD2DSS of the smallest synchronization signal relay hop number to timeresources precedent to D2DSSs of different synchronization signal relayhop number and then sequentially allocate the D2DSSs to the timeresources in order in which the synchronization signal relay hop numberincreases. In certain embodiments, the largest synchronization signalrelay hop number are previously defined in a system or configured by acentral control subject. The terminal recognizes the synchronizationsignal relay hop number corresponding to the relevant D2DSS through thereceived D2DSS. The terminal determines D2DSS time resources ofdifferent synchronization signal relay hop numbers based on therecognized synchronization signal relay hop number and the receivedD2DSS time resources. When the terminal performs the synchronizationsignal relay hop based on the received D2DSS, the terminal generates aD2DSS of the synchronization signal relay hop number corresponding tothis and transmits the D2DSS using the time resources of thecorresponding hop number.

If the received D2DSS indicates the largest synchronization signal relayhop number, the terminal cannot perform the synchronization signal relayhop any longer. In addition, the terminal generates a D2DSS of thesmallest synchronization signal relay hop number and performs a newsynchronization signal relay hop by transmitting the D2DSS using timeresources corresponding to the new synchronization signal.

In a second method, a mapping rule is previously defined to map a D2DSSof the largest synchronization signal relay hop number to time resourcesprecedent to D2DSSs of different synchronization signal relay hop numberand then sequentially to allocate the D2DSSs to the time resources inorder in which the synchronization signal relay hop number decreases.

The terminal recognizes the synchronization signal relay hop numbercorresponding to the relevant D2DSS through the received D2DSS. Theterminal determines D2DSS time resources of different synchronizationsignal relay hop number based on the recognized synchronization signalrelay hop number and the received D2DSS time resources. When theterminal performs the synchronization signal relay hop based on thereceived D2DSS, the terminal generates a D2DSS of the synchronizationsignal relay hop number corresponding to received D2DSS and transmitsthe D2DSS using time resources of the corresponding hop number.

If the received D2DSS indicates the smallest synchronization signalrelay hop number, the terminal cannot perform the synchronization signalrelay hop any longer or performs a new synchronization signal relay hopby generating a D2DSS of the largest synchronization signal relay hopnumber and transmitting the D2DSS using time resources corresponding tothe received D2DSS.

In the aforementioned mapping rules, a time resource interval betweenD2DSSs of different synchronization signal relay hop numbers can becontinuous or dispersible.

A method of designing a Device-to-Device Synchronization Signal (D2DSS)according to an embodiment of the present disclosure is to divide a setof root index values which at least one sequence constituting the D2DSS,for example the second sequence 103, can have into a plurality ofsubsets. The divided subsets correspond to the types of D2DSStransmission subjects one-to-one. For example, a set of root indices,which a current LTE base station can use when generating a PrimarySynchronization Signal (PSS), is constituted by 25, 29, and 34. Ingenerating the second sequence 103 of the D2DSS, a separate set can bedefined and used which is constituted by a root index, which thecellular network base station can use, and at least one other root indexvalue.

For example, the second sequence 103 of the D2DSS transmitted by aterminal outside the cellular network service region can be generatedusing the root index pertaining to the separate set. The second sequenceof the D2DSS transmitted by a terminal inside the cellular networkservice region can be generated using the root index value which thebase station has used when transmitting a PSS. Alternatively, a separateset can be defined that is constituted by other root index values otherthan the root indices, which are used by the aforementioned basestations 25, 29, and 34, and can be divided into subsets correspondingto the types of D2DSS transmission subjects one-to-one.

The D2DSS signal according to certain embodiments is designed in adifferent way to inform of the number of D2DSS relay hops fortransmission thereof. For example, the set of root indices or therespective root index values are divided into subsets corresponding tothe D2DSS relay hop number, and each of the subsets corresponds to theD2DSS relay hop number corresponding to the D2DSS one-to-one. Forexample, root indices 25, 29, and 34 correspond to the D2DSS relay hopnumber 0, 1, and 2, respectively.

In methods of designing a D2DSS according to certain embodiments of thepresent disclosure, locations of physical layer resources to which atleast one sequence constituting the D2DSS, for example the firstsequence 100, is mapped can be differently defined according to the typeof D2DSS transmission subject. For example, two short m-sequencesconstituting the first sequence 100 of the D2DSS can be defined as shownin Equation 1. The first sequence 100 generated and mapped according toEquation 1 can be used when the terminal inside the cellular networkservice region generates the D2DSS.

In contrast, when the terminal outside the cellular network serviceregion generates the D2DSS, the first sequence 100 can be generated andmapped according to Equation 2 defined below.

$\begin{matrix}{{d\left( {{2n} + 1} \right)} = \left\{ {{\begin{matrix}{{s_{0}^{(m_{0})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 0} \\{{s_{1}^{(m_{1})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu} {subframe}{\mspace{11mu} \;}5}\end{matrix}{d\left( {2n} \right)}} = \left\{ \begin{matrix}{{s_{1}^{(m_{1})}(n)}{c_{1}(n)}{z_{1}^{(m_{0})}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 0} \\{{s_{0}^{(m_{0})}(n)}{c_{1}(n)}{z_{1}^{(m_{1})}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 5}\end{matrix} \right.} \right.} & {{Equation}\mspace{14mu} 2}\end{matrix}$

The definitions of variables in Equation 2 are the same as those inEquation 1. Equations 1 and 2 are different from each other in that thesignals transmitted to even and odd subcarriers are switched to eachother at a time point of transmitting two D2DSSs within a radio frame.That is, the case in which the first sequence 100 is generated andmapped according to the Equation 1 when the D2DSS is generated and thecase in which the first sequence 100 is generated and mapped accordingto Equation 2 can correspond to generation and snapping of the D2DSSfirst sequence 100 of the terminal inside the cellular network serviceregion and the D2DSS first sequence 100 of the terminal outside thecellular network service region. The aforementioned methods are notlimited to these embodiments, and the definition can be made with thecorresponding relation changed.

In methods of designing a D2DSS according to certain embodiments of thepresent disclosure, it is possible to differently define locations ofrelative frequency resources to which at least two sequences constitutethe D2DSS, such as the first sequence 100 and the second sequence 103are mapped according to the type of D2DSS transmission subject. Forexample, in the D2DSS of the terminal inside the cellular networkservice region, the first sequence 100 and the second sequence 103 aretransmitted to locations that are the same in frequency but different intime. Meanwhile, in the D2DSS of the terminal outside the cellularnetwork service region, the first sequence 100 and the second sequence103 are transmitted to locations that are different in time andfrequency. In certain embodiments, a difference in relative frequencylocation between the two sequences is the predetermined number ofsubcarriers or an RB value.

The D2DSS signal according to the embodiment can be designed in adifferent way to inform the number of D2DSS relay hops for transmissionthereof. For example, if the D2DSS is mapped through the plural methodsas described above, each of the mapping methods can correspond to theD2DSS relay hop number corresponding to the D2DSS one-to-one.

The root index and the combination indices of m₀ and m₁ used todistinguish the type of D2DSS transmission subject when the firstsequence 100 or the second sequence 103 is generated in theaforementioned D2DSS design methods are used for various applications,such as an input of an initialization function in generating ascrambling sequence used in D2D physical channel transmission orreception, an input of a Demodulation Reference Signal (DMRS) generationfunction of a D2D physical channel, and an input of a time or frequencyhop location definition function of a D2D physical channel and signal.In addition, the root index and the combination indices of m₀ and m₁ canbe used to inform an ID of the corresponding D2DSS transmission subjectindependently or in combination of two indices.

Based on the aforementioned D2DSS design methods, a terminal can receivea D2DSS from another terminal or generate and transmit a D2DSS toanother terminal. A method of using a D2DSS designed using the methodswill be described below in more detail.

FIG. 2 illustrates an exemplary process for detecting a synchronizationsignal according to embodiments of the present disclosure. Referring toFIG. 2, a terminal receives a synchronization signal in step 200. Thesynchronization signal can be a PSS or SSS transmitted by a basestation, a synchronization signal transmitted by another terminal insidea service region, or a synchronization signal transmitted by anotherterminal outside the service region. A plurality of types ofsynchronization signals is received. In this case, the terminal performsa synchronization operation according to a preconfigured priority orderas will be described below.

In step 205, the terminal determines a subject having transmitted thesynchronization signal, based on the received synchronization signal.Since the PSS or SSS transmitted by a base station is distinguished fromD2DSSs transmitted by other terminals, the terminal can detect the PSSor SSS. In addition, since a synchronization signal transmitted by aterminal inside the service area and a synchronization signaltransmitted by a terminal outside the service area are designed to bedistinguished from each other according to the aforementioned D2DSSdesign method, the terminal distinguishes the synchronization signals.The terminal distinguishes the type of synchronization signal and when aplurality of synchronization signals are received and determines thesynchronization signal serving as a timing reference, depending upon thepriorities thereof. In certain embodiments, when selecting the timingreference of the subject having transmitted the synchronization signal,the terminal makes a configuration such that a PSS or SSS transmitted bya base station has the highest priority, a D2DSS transmitted by aterminal inside a cellular network service region has the intermediatepriority, and a D2DSS transmitted by a terminal outside the cellularnetwork service region has the lowest priority. This embodiment ismerely exemplary, and the present disclosure is not limited thereto.

In step 210, the terminal performs a synchronization operation, based onthe received synchronization signal. In certain embodiments, thesynchronization operation is an operation of identically orcorrespondently adjusting the synchronization of the terminal based onthe timing reference, determined by the terminal, among the receivedsynchronization signals. In addition, the synchronization operation caninclude an operation of transmitting a new D2DSS based on the determinedtiming reference.

Next, various embodiments of detecting and using a synchronizationsignal will be described with reference to FIGS. 3-8. Hereinafter, astep for detecting a PSS or SSS transmitted by a base station, a stepfor detecting a D2DSS transmitted by a terminal inside a network serviceregion, and a step for detecting a D2DSS transmitted by a terminaloutside the network service region are separately illustrated in FIGS.3-8 in a similar way.

However, the embodiments of the present disclosure are not limited todifferentiating the synchronization signal detection steps. That is, asillustrated in FIGS. 3-8, synchronization signals can also be detectedin separate steps, respectively. In addition, a determination can alsobe made as to ether a synchronization signal of a signal receivedthrough one procedure corresponds to a synchronization signaltransmitted by a base station, a synchronization signal transmitted by aterminal inside a service region, or a synchronization signaltransmitted by a terminal outside the service region. Furthermore, aprocedure of detecting a synchronization signal of a base station and aprocedure of detecting a synchronization signal transmitted by anotherterminal can be separately configured, and in the procedure of detectinga synchronization signal, a determination can also be made as to whetherthe synchronization signal transmitted by the another terminal is asignal transmitted by a terminal inside a service region or a signaltransmitted by a terminal outside the service region.

FIG. 3 illustrates an exemplary process for detecting and transmitting aD2DSS according to embodiments of the present disclosure. Referring toFIG. 3, a terminal receives a signal transmitted by a base station oranother terminal and detects a synchronization signal.

In step 300, the terminal attempts to detect PSS or SSS, which istransmitted from a base station, from a signal received thorough adownlink. The detection can be performed for a preset period of time. Ifa PSS or SSS is not detected for the preset period of time or the presetnumber of detection attempts, the corresponding terminal recognizes thata base station capable of providing a cellular network service is notpresent, and proceeds to step 305.

In step 305, the corresponding terminal attempts to detect a D2DSStransmitted by a terminal inside a cellular network service region. Thedetection can be performed for a preset period of time. In certainembodiments, the corresponding terminal attempts to detect a D2DSS usingone of the D2DSS design methods, described as embodiments of the presentdisclosure, transmitted by a terminal inside the aforementioned cellularnetwork service region. If no D2DSS is detected for the preset period oftime or the number of detection attempts, the terminal recognizes thatthere is no adjacent cellular network service region, and proceeds tostep 310.

In step 310, the corresponding terminal attempts to detect a D2DSStransmitted by a terminal outside the cellular network service region.In certain embodiments, the corresponding terminal attempts to detect aD2DSS using one of the D2DSS design methods (the D2DSS design methodsmentioned as the embodiments of the present disclosure prior to thedescription of FIG. 2) transmitted by a terminal outside theaforementioned cellular network service region. If no D2DSS is detectedduring a preset period of time or the number of detection attempts, thecorresponding terminal recognizes that a subject capable of providingsynchronization is not present.

When the terminal receives no synchronization signal transmitted from abase station or any other terminal in the step 310, the terminalproceeds to step 315 to transmit a D2DSS according to the timingreference thereof. In certain embodiments, the terminal transmitting theD2DSS transmits a D2DSS designed on the basis of the aforementioned.D2DSS design method of distinguishing subjects of transmission. Forexample, the reason the terminal fails to receive a PSS or SSS from abase station in step 300 can be because the terminal is located outsidethe service region of the base station. Therefore, the terminalgenerates a D2DSS transmitted by a terminal outside the service regionand transmits the generated D2DSS.

In certain embodiments of the present disclosure, where the terminalsucceeds in detecting a synchronization signal in at least one of steps300, 305, and 310, the corresponding terminal proceeds to step 320 totransmit a D2DSS using the timing reference obtained from the detectedsynchronization signal. For example, when the terminal detects a PSS orSSS from a base station in step 300, the terminal generates a D2DSSbased on the PSS or SSS detected from the base station and transmits thegenerated D2DSS to other terminals, in step 315. When the terminaldetects a D2DSS from a terminal inside the service region of the basestation in step 305, the terminal transmits the D2DSS signal generatedbased on the detected D2DSS to other terminals. In addition, when theterminal detects a D2DSS from a terminal outside the service region ofthe base station in step 310, the terminal transmits the D2DSS signalgenerated based on the detected D2DSS to other terminals.

In certain embodiments of the present disclosure, where a plurality ofsynchronization signals are detected, the terminal recognizes thesubject having transmitted each of the synchronization signals, whendetecting the corresponding synchronization signal through theaforementioned DSDSS design methods, and selects the timing reference ofthe synchronization signal by which the D2DSS is to be transmitted,based on the recognized subject.

When the timing reference of the subject transmitting thesynchronization signal is selected, the base station has the highestpriority, a D2DSS transmitted by a terminal inside a cellular networkservice region has the next highest priority, and a D2DSS transmitted bya terminal outside the cellular network service has the lowest priority.The reason for prioritizing the synchronization signal is to alleviate,as soon as possible, interference between a cellular uplink signal and aD2D signal, which is caused by different timing references, by inducingD2D terminals to share the timing reference used inside the cellularnetwork service region that is the main service target when an LTEsystem supporting the cellular service additionally supports D2Dcommunication. However, this embodiment is merely an exemplaryembodiment, and the selection of the timing reference is not necessarilylimited thereto. For example, the strength of the detectedsynchronization signal can also be further considered.

FIG. 4 illustrates an exemplary process for detecting a synchronizationsignal and performing synchronization configuration according to anembodiment of the present disclosure. Referring to FIG. 4, the steps400, 405, and 410 are similar to the steps 300, 305, and 310 illustratedin FIG. 3, respectively.

In step 400, a terminal attempts to detect a PSS or SSS from a basestation received. through a downlink. If a PSS or SSS is not detectedfor a preset period of time or the preset number of detection attempts,the corresponding terminal recognizes that a base station capable ofproviding a cellular network service is not present and proceeds to step405.

In step 405, the corresponding terminal attempts to detect a D2DSStransmitted by a terminal inside a cellular network service region. Incertain embodiments, the corresponding terminal attempts to detect theD2DSS using one D2DSS design method transmitted by the aforementionedterminal inside the cellular network service. If no D2DSS is detectedduring a preset period of time or the number of detection attempts, theterminal recognizes that there is no adjacent cellular network serviceregion and proceeds to step 410 to attempt to detect a D2DSS transmittedby a terminal outside the cellular network service region. In certainembodiments, the corresponding terminal attempts to detect the D2DSSusing one D2DSS design method transmitted by the aforementioned terminaloutside the cellular network service. If no D2DSS is detected during apreset period of time or the number of detection attempts, thecorresponding terminal recognizes that a subject capable of providingsynchronization is not present and proceeds to step 415.

The terminal fails to receive or detect a synchronization signal forconfiguring a timing reference for synchronization in steps 400, 405,and 410 and generates a synchronization signal based on the timingreference thereof and transmit the generated synchronization signal toother terminals there around in step 415. In certain embodiments, thereason why the terminal fails to detect PSS or SSS from the downlinksignal transmitted from the base station in step 400 can be determinedthat the terminal is located outside the service region of the basestation. Therefore, the terminal transmits the generated D2DSS to otherterminals, based on the D2DSS design method transmitted by a terminaloutside the service region.

In cases where the terminal succeeds in detecting a synchronizationsignal in at least one of steps 400, 405, and 410, the correspondingterminal can proceed to step 420 to fit the synchronization using thetiming reference obtained from the detected synchronization signal. Incertain embodiments, in cases where a plurality of synchronizationsignals are detected, the terminal recognizes the subject havingtransmitted each of the synchronization signals when detecting thecorresponding synchronization signal through the aforementioned DSDSSdesign methods and selects the timing reference of the synchronizationsignal by which the synchronization is to be performed based on therecognized subject. As in step 420, the terminal cannot act as a relayand can also use the received synchronization signal only for fittingthe synchronization thereof.

FIG. 5 illustrates an exemplary process for detecting and transmitting asynchronization signal according to embodiments of the presentdisclosure.

In step 500, a terminal attempts to detect a PSS or SSS from a basestation received through a downlink. If a PSS or SSS is not detected fora preset period of time or the preset number of detection attempts, thecorresponding terminal recognizes that a base station capable ofproviding a cellular network service is not present and proceeds to step505.

In step 505, the corresponding terminal attempts to detect a D2DSS (TypeA D2DSS) transmitted by a terminal inside a cellular network serviceregion. In certain embodiments, the corresponding terminal attempts todetect the D2DSS using one of the aforementioned D2DSS design methods.If a Type A D2DSS is not detected during a preset period of time or thenumber of detection attempts, the terminal recognizes that there is noadjacent cellular network service region and proceeds to step 510.

In step 510, the corresponding terminal attempts to detect a D2DSS (TypeB D2DSS) transmitted by a terminal outside the cellular network serviceregion. In certain embodiments, the corresponding terminal attempts todetect the D2DSS using one of the aforementioned D2DSS design methods.If a Type B D2DSS is not detected during a preset period of time or thenumber of detection attempts, the corresponding terminal recognizes thata subject capable of providing synchronization is not present andproceeds to step 515.

In step 515, the corresponding terminal transmits the D2DSS according tothe timing reference thereof. In certain embodiments, the D2DSStransmitted by the corresponding terminal can be a Type B D2DSS, becausethe corresponding terminal transmits the D2DSS outside the networkservice region. Since the terminal fails to detect a PSS or SSS from thedownlink transmitted from the base station in step 500, a determinationis made that the terminal is present outside the service region.

When succeeding in detecting the synchronization signal in step 500, thecorresponding terminal proceeds to step 520 to fit the synchronizationusing the timing reference obtained from the detected synchronizationsignal. In certain embodiments, the D2DSS transmitted by thecorresponding terminal is a Type A D2DSS, because the correspondingterminal transmits the D2DSS inside the network service region. Sincethe terminal detects a PSS or SSS from the downlink transmitted from thebase station, it is determined that the terminal is present inside theservice region of the base station.

In cases where the terminal succeeds in detecting a synchronizationsignal in at least one of steps 505 and 510, the corresponding terminalproceeds to step 525 to transmit the D2DSS using the timing referenceobtained from the detected synchronization signal. In certainembodiments, the D2DSS transmitted by the corresponding terminal is aType B D2DSS, because the corresponding terminal transmits the D2DSSoutside the network service region.

FIG. 6 illustrates an exemplary process for detecting and transmitting asynchronization signal according to embodiments of the presentdisclosure.

In step 600, a terminal attempts to detect a PSS or SSS from a basestation received through a downlink. If a PSS or SSS is not detected fora preset period of time or the preset number of detection attempts, thecorresponding terminal recognizes that a base station capable ofproviding a cellular network service is not present and proceeds to step605.

In step 605, the corresponding terminal attempts to detect a Type A′D2DSS transmitted by a terminal according to the synchronizationreference inside a cellular network service region. In certainembodiments, the corresponding terminal attempts to detect the D2DSSusing one of the aforementioned D2DSS design methods. If no Type A′D2DSS is detected during a preset period of time or the number ofdetection attempts, the terminal recognizes that there is no adjacentcellular network service region and proceeds to step 610.

In step 610, the corresponding terminal attempts to detect a Type B′D2DSS transmitted by a terminal which does not conform thesynchronization reference inside the cellular network service region. Incertain embodiments, the corresponding terminal attempts to detect theD2DSS using one of the aforementioned D2DSS design methods. If no TypeB′ D2DSS is detected during a preset period of time or the number ofdetection attempts, the corresponding terminal recognizes that a subjectcapable of providing synchronization is not present and proceeds to step615.

In step 615, the corresponding terminal transmits the D2DSS according tothe timing reference thereof. In certain embodiments, the D2DSStransmitted by the corresponding terminal is a Type B′ D2DSS, becausethe corresponding terminal transmits the D2DSS while not conforming tothe timing reference inside the network service region.

In the case where the terminal succeeds in detecting a synchronizationsignal in at least one of steps 600 and 605, the corresponding terminalproceeds to step 620 to fit the synchronization using the timingreference obtained from the detected synchronization signal. In certainembodiments, the D2DSS transmitted by the corresponding terminal is aType A′ D2DSS, because the corresponding terminal transmits the D2DSSwhile conforming to the timing reference inside the network serviceregion.

When succeeding in detecting the synchronization signal in step 610, thecorresponding terminal proceeds to step 625 to transmit the D2DSS usingthe timing reference obtained from the detected synchronization signal.In certain embodiments, the D2DSS transmitted by the correspondingterminal is a Type B′ D2DSS, because the corresponding terminaltransmits the D2DSS while not conforming to the timing reference insidethe network service region.

FIG. 7 illustrates an exemplary process for detecting a synchronizationsignal and transmitting the synchronization signal based on a hop numberaccording to embodiments of the present disclosure.

In step 700, a terminal attempts to detect a PSS or SSS from a basestation received through a downlink. If a PSS or SSS is not detected fora preset period of time or the preset number of detection attempts, thecorresponding terminal recognizes that a base station capable ofproviding a cellular network service is not present and proceeds to step705.

In step 705, the corresponding terminal attempts to detect a D2DSStransmitted by another terminal. In certain embodiments, thecorresponding terminal attempts to detect the D2DSS using one of theaforementioned D2DSS design methods. If no D2DSS is detected during apreset period of time or the number of detection attempts, thecorresponding terminal recognizes that a subject capable of providingsynchronization is not present and proceeds to step 710 to transmit theD2DSS according to the timing reference thereof.

When succeeding in detecting the synchronization signal in step 700, thecorresponding terminal proceeds to step 715 to fit the synchronizationusing the timing reference obtained from the detected synchronizationsignal and transmit the D2DSS. In this certain embodiments, the D2DSStransmitted by the corresponding terminal is generated to correspond tothe lowest synchronization signal relay hop number, for example asynchronization signal relay hop number 1.

When succeeding in detecting the synchronization signal in step 705, thecorresponding terminal proceeds to step 720 to transmit the D2DSS usingthe timing reference based on the D2DSS having the lowestsynchronization signal relay hop number among the detected D2DSSs. Inthis case, the D2DSS transmitted by the corresponding terminal can begenerated to correspond to a synchronization signal relay hop number avalue of 1 greater than the synchronization signal relay hop numberrepresented by the D2DSS which the corresponding terminal detects andcurrently uses as the timing reference for the transmission of theD2DSS.

FIG. 8 illustrates an exemplary process for detecting a synchronizationsignal and transmitting the synchronization signal based on a receptionlevel according to embodiments of the present disclosure.

In step 800, a terminal attempts to detect a PSS/SSS from a base stationreceived through a downlink. If a PSS or SSS is not detected for apreset period of time or the preset number of detection attempts or thereception level of the detected signal is lower than a preconfiguredthreshold value, the corresponding terminal recognizes that a basestation capable of providing a cellular network service is not presentand proceeds to step 805.

In step 805, the corresponding terminal attempts to detect a Type AD2DSS transmitted by a terminal inside a cellular network serviceregion. In certain embodiments, the corresponding terminal attempts todetect the D2DSS using one of the aforementioned D2DSS design methods.If no Type A D2DSS is detected during a preset period of time or thenumber of detection attempts or the reception level of the detectedsignal is lower than a preconfigured threshold value, the terminalrecognizes that there is no adjacent cellular network service region andproceeds to step 810.

In step 810, the corresponding terminal attempts to detect a Type BD2DSS transmitted by a terminal outside the cellular network serviceregion. In certain embodiments, the corresponding terminal attempts todetect the D2DSS using one of the aforementioned D2DSS design methods.If no Type B D2DSS is detected during a preset period of time or thenumber of detection attempts or the reception level of the detectedsignal is lower than a preconfigured threshold value, the correspondingterminal recognizes that a subject capable of providing synchronizationis not present and proceeds to step 815.

In step 815, the terminal transmits the D2DSS according to the timingreference thereof. In certain embodiments, the D2DSS transmitted by thecorresponding terminal is a Type B D2DSS, because the correspondingterminal transmits the D2DSS outside the network service region.

When the terminal succeeds in detecting the synchronization signal andthe reception level of the detected signal is higher than or equal tothe preconfigured threshold value in step 800, the correspondingterminal proceeds to step 820 to fit the synchronization using thetiming reference obtained from the detected synchronization signal. Incertain embodiments, the D2DSS transmitted by the corresponding terminalis a Type A D2DSS, because the corresponding terminal transmits theD2DSS inside the network service region.

When the terminal succeeds in detecting the synchronization signal andthe reception level of the detected signal is higher than or equal tothe preconfigured threshold value in at least one of steps 805 and 810,the corresponding terminal proceeds to step 825 to transmit the D2DSSaccording to the timing reference obtained from the detectedsynchronization signal. In certain embodiments, the D2DSS transmitted bythe corresponding terminal is a Type B D2DSS, because the correspondingterminal transmits the D2DSS outside the network service region. Theprocess of adding, as a timing reference determination condition, thedetermination as to whether the reception level of the detectedsynchronization signal is higher than or equal to the preconfiguredthreshold value can be applied to all the embodiments illustrated inFIGS. 3-7.

The D2DSS design method described above with reference to FIG. 1 can beapplied to all the embodiments illustrated in FIGS. 2-8. In addition, itis apparent to those skilled in the art that the contents of each of theembodiments described in FIGS. 2-8 can be applied to the differentembodiments.

FIG. 9 illustrates a block diagram of a reception block of a D2DSStransmission terminal according to embodiments of the presentdisclosure. The embodiment of the block diagram shown in FIG. 9 is forillustration only. Other embodiments could be used without departingfrom the scope of the present disclosure.

The reception block includes a controller 900, a synchronization signaldetection unit 901, and a timing reference selection unit 902.

The controller 900 controls the transmission terminal to perform theoperations in one of the aforementioned embodiments and configurescontrol information on a PSS or SSS, a D2DSS of a terminal inside anetwork service region, a D2DSS of a terminal outside the networkservice region, and on the selection of the timing reference. Thesynchronization signal detection unit 901 detects the PSS or SSS, theD2DSS of the terminal inside the network service region, and the D2DSSof the terminal outside the network service region according to thecontrol information configured by the controller 900.

The timing reference selection unit 902 performs a function ofdetermining the timing reference to be used when a terminal transmits aD2DSS, from the synchronization signal detected by the synchronizationsignal detection unit 901. In certain embodiments, the timing referenceselection unit 902 complies with the timing reference selection methodconfigured by the controller 900.

FIG. 10 illustrates a block diagram of a transmission block of a D2DSStransmission terminal according to embodiments of the presentdisclosure. The embodiment of the transmission block shown in FIG. 10 isfor illustration only. Other embodiments could be used without departingfrom the scope of the present disclosure.

The transmission block includes a controller 1000, a D2DSS generationunit 1001, a D2DSS resource mapping unit 1002, and a D2DSS signaltransmission unit 1003.

The controller 1000 controls the transmission terminal to perform theoperations in any of the aforementioned embodiments. The D2DSSgeneration unit 1001 generates an appropriate D2DSS depending upon thecontrol information, which the controller 1000 has configured inconsideration of the type of synchronization signal transmission subjectof the corresponding terminal. The D2DSS resource mapping unit 1002maps, to a physical layer resource, the D2DSS generated depending uponthe control information, which the controller 1000 has configured inconsideration of the type of synchronization signal transmission subjectof the corresponding terminal. The D2DSS signal transmission unit 1003transmits the D2DSS according to the control information configured bythe controller 1000 on the basis of the timing reference obtained byreceiving another synchronization signal before the transmission of theD2DSS.

The reception block and the transmission block have been described abovewith reference to FIGS. 9 and 10, respectively. However, this is toseparately describe the transmission operation and the receptionoperation of the terminal, and the transmission and reception blocks donot necessarily operate separately.

For example, a terminal can also be expressed with a transmission orreception unit for transmitting or receiving a signal to or from atleast one base station or terminal and a controller for controlling theoverall operation thereof. In certain embodiments, it is apparent thatthe controller can control the operation of each component in thereception block and the operation of each component in the transmissionblock.

According to embodiments of the present disclosure, the controllerdetermines a service attribute for identifying whether the terminal isserviced by at least one base station, and controls the terminal togenerate a D2DSS capable of identifying whether the terminal is servicedby the base station, based on the determination result. In certainembodiments, the service attribute is information for indicating whetherthe terminal is serviced by the base station, whether the terminalreceives a signal from another terminal within the service range of thebase station, and whether the terminal receives a signal from anotherterminal beyond the service range of the base station.

In certain embodiments, the controller configures a set of cyclic shiftvalues, which at least one sequence constituting the D2DSS can have, asat least two subsets, makes a configuration such that the at least twosubsets correspond to the service attributes of the terminal, and makesa control to generate at least one sequence constituting the D2DSS,based on elements contained in the subsets corresponding to the serviceattributes of the terminal.

In certain embodiments, the controller configures a set of root indexvalues, which at least one Zadoff-Chu (ZC) sequence constituting theD2DSS can have, as at least two subsets, makes a configuration such thatthe at least two subsets correspond to the service attributes of theterminal, and makes a control to generate at least one ZC sequenceconstituting the D2DSS, based on elements contained in the subsetscorresponding to the service attributes of the terminal.

In certain embodiments, the controller differently configures thelocations of physical layer resources, to which one or more sequencesconstituting the D2DSS are mapped, according to the service attributes,and makes a control to map the one or more sequences constituting theD2DSS to the locations of the physical layer resources corresponding tothe service attributes of the terminal.

In certain embodiments, the controller differently configures therelative locations of physical layer resources, to which at least twosequences constituting the D2DSS are mapped, according to the serviceattributes, and makes a control to map the at least two sequencesconstituting the D2DSS to the relative locations of the physical layerresources corresponding to the service attributes of the terminal.

In certain embodiments, the controller receives a D2DSS from at leastone other terminal, determines the order of a synchronization signalrelay hop corresponding to the received D2DSS, and makes a control togenerate a new D2DSS based on the service attributes and the informationon the synchronization signal relay hop of the received D2DSS.

In certain embodiments, the controller receives a signal from the atleast one base station or another device, determines whether asynchronization signal is detected from the received signal, and makes acontrol to configure synchronization with another device based on thetiming reference of the detected synchronization signal when thesynchronization signal is detected.

In certain embodiments, the controller makes a control to generate aDevice-to-Device Synchronization Signal (D2DSS) based on the timingreference of the detected synchronization signal when thesynchronization signal is detected. The controller makes a control togenerate a new D2DSS according to the timing reference of the terminal,when the synchronization signal is not detected.

In certain embodiments, the controller determines whether thesynchronization signal transmitted by a base station is detected. Whenthe synchronization signal transmitted by the base station is notdetected, the controller determines whether the synchronization signaltransmitted by another device is detected. In addition, the controllerdetermines whether the D2DSS transmitted by a device inside a networkservice region is detected. When the D2DSS transmitted by the deviceinside the network service region is not detected, the controllerdetermines whether the D2DSS transmitted by a device outside the networkservice region is detected.

In certain embodiments, the controller lakes a control to generate aD2DSS corresponding to the type of synchronization signal of a terminalinside a service region when the detected synchronization signal is asynchronization signal received from a base station, and makes a controlto generate a D2DSS corresponding to the type of synchronization signalof a terminal outside the service region when the detectedsynchronization signal is a synchronization signal received from anotherdevice.

In certain embodiments, the controller makes a control to allocate thereceived D2DSS to a time resource based on the hop information whengenerating the new D2DSS. In certain embodiments, the controller appliesthe aforementioned Time Division Multiplexing (TDM) method.

In certain embodiments, the controller makes a control to generate aD2DSS corresponding to the type of synchronization signal of a terminalinside a service region when the detected synchronization signal is asynchronization signal received from a base station or a synchronizationsignal received from a device inside the service region, and makes acontrol to generate a D2DSS corresponding to the type of synchronizationsignal of a terminal outside the service region when the detectedsynchronization signal is a synchronization signal received from adevice outside the service region.

In certain embodiments, the controller makes a control to generate a newD2DSS according to the timing reference of the terminal corresponding tothe type of synchronization signal of a terminal outside the serviceregion. The controller determines the number of D2D relays through whichthe detected synchronization signal has been received and makes acontrol to generate a D2DSS based on the timing reference of thesynchronization signal received through the smallest number of D2Drelays. The controller determines whether the reception signal strengthfor the detected synchronization signal is greater than or equal to apreconfigured threshold value, and makes a control to generate a D2DSSaccording to the timing reference of the synchronization signal detectedfrom signals having a reception signal strength of the preconfiguredthreshold value or greater.

The operations of the controller of the terminal according to theembodiment of the present disclosure have been described above. However,these are only for convenience of description, and the presentdisclosure is not necessarily limited thereto. In addition, thecontroller can control the operations of the terminal proposed in thesynchronization configuration method, the synchronization signal designmethod, the synchronization detection method, and the synchronizationsignal transmission method according to the present disclosure, whichhave been described with reference to FIGS. 1-8.

Although the embodiments to which the 3GPP LTE uplink based transmissionmethod is applied have been described above, the present disclosure isnot limited thereto and may also be applied to other transmissionmethods.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1-20. (canceled)
 21. A method by a terminal in a wireless communicationsystem, the method comprising: generating a synchronization signal fordevice to device (D2D) communication; and transmitting thesynchronization signal to at least one device, wherein thesynchronization signal is generated based on a first root index if theterminal is in a coverage of a base station, and wherein thesynchronization is generated based on a second root index if theterminal is out of the coverage of the base station.
 22. The method ofclaim 21, wherein the first root index and the second root index aredifferent from a root index used by the base station.
 23. The method ofclaim 21, wherein a sequence for the synchronization signal is generatedbased on one of the first root index and the second root index.
 24. Themethod of claim 21, wherein the synchronization signal is generatedbased on information received from the base station if the terminal isin the coverage of the base station.
 25. The method of claim 21, whereinthe D2DSS is generated based on the second root index if the terminal isout of the coverage of the base station and another terminal is notdetected for synchronization reference.
 26. A terminal in a wirelesscommunication system, the terminal comprising: a transceiver configuredto transmit and receive a signal; and a controller configured to:generate a synchronization signal for device to device (D2D)communication, and transmit the synchronization signal to at least onedevice, wherein the synchronization signal is generated based on a firstroot index if the terminal is in a coverage of a base station, andwherein the synchronization is generated based on a second root index ifthe terminal is out of the coverage of the base station.
 27. Theterminal of claim 26, wherein the first root index and the second rootindex are different from a root index used by the base station.
 28. Theterminal of claim 26, wherein a sequence for the synchronization signalis generated based on one of the first root index and the second rootindex.
 29. The terminal of claim 26, wherein the synchronization signalis generated based on information received from the base station if theterminal is in the coverage of the base station.
 30. The terminal ofclaim 26, wherein the D2DSS is generated based on the second root indexif the terminal is out of the coverage of the base station and anotherterminal is not detected for synchronization reference.